I'm insured with HIC and all I have to do is tell them I'm going on a Trackday and I'm covered (albeit with a £1k excess ) - Its all part of the policy that just happened to be by far the cheapest I found (taking modifications into account).

Just about got the insurance sorted - AON want to know if the event will be fully marshaled and non-competitive, closed pit (by which I take it they mean only those and such as those are allowed to participate) and flagged and how many cars on track at a time.